Method for discriminating x-ray contrast image from non-contrast image and x-ray imaging system including contrast image discriminating function

Abstract

To discriminate a contrast image from a non-contrast image, an X-ray imaging method is characterized by comprising the steps of: acquiring a plurality of X-ray images of a biological body under medical examination; subtracting at least two sets of the X-ray images with each other acquired at temporally different timings to obtain a subtraction image; subdividing one subtraction image into a plurality of image blocks; calculating an averaged value of image concentration with respect to each of the image blocks, thereby obtaining a plurality of averaged values for the subdivided image blocks; calculating a difference between at least two averaged values of image concentration with respect to the image blocks acquired within substantially same temporal timing period; and, judging whether or not the X-ray image is acquired under such a condition that an X-ray contrast medium appears therein based upon the difference in said two averaged values of image concentration.

what is claimed is: 
     
       1. An X-ray imaging method comprising the steps of: acquiring a plurality of X-ray images of a biological body under medical examination;   subtracting at least two of the X-ray images from each other acquired at temporally different timings to obtain a subtraction image;   subdividing one subtraction image into a plurality of image blocks;   calculating an averaged value of image concentration with respect to each of the image blocks, thereby obtaining a plurality of averaged values for each of the plurality of image blocks;   calculating a difference between at least two of said charged values of image concentration with respect to the image blocks acquired within substantially same temporal timing period; and,   judging whether one of said plurality of X-ray images is acquired under such a condition that an X-ray contrast medium appears therein based upon the difference in said two averaged values of image concentration.   
     
     
       2. An X-ray imaging method as claimed in claim 1, further comprising the step of: coding said averaged value of image concentration for the image blocks by comparing said averaged value with a threshold value to obtain coded-image data, whereby it is judged whether the X-ray image is acquired under such a condition that an X-ray contrast medium appears therein based n the coded image data.   
     
     
       3. An X-ray imaging method as claimed in claim 2, wherein at least two different threshold values are employed. 
     
     
       4. An X-ray imaging method as claimed in claim 1, wherein said one subtraction image is subdivided into at least four image blocks. 
     
     
       5. An X-ray imaging system comprising: means for producing a plurality of X-ray images of a biological body under medical examination;   subtraction means for subtracting at least two of the X-ray images with each of the produced at temporally different timings to obtain a subtraction image;   subdividing means or subdividing said subtraction image into a plurality of image blocks;   averaging means for obtaining an averaged value of image concentration for each of image blocks subdivided from one subtraction image, thereby obtaining a plurality of averaged values for the image blocks;   calculating means for calculating a difference between at least two of said averaged values of image concentration with respect to the image blocks acquired within substantially same temporal timing period; and   judging means for judging whether one of the plurality of X-ray times is acquired under such a condition that an X-ray contrast medium appears therein based upon the difference in said two averaged values of image concentration.   
     
     
       6. An X-ray imaging system as claimed in claim 5, wherein said averaging means is constructed of at least accumulating means for accumulating said plurality of X-ray images, and subtracting means for performing a subtraction among the accumulated X-ray images, whereby said averaged values of image concentration are obtained. 
     
     
       7. An X-ray imaging system as claimed in claim 5, wherein said calculating means includes: threshold value generating means for generating at least a first threshold value and a second threshold value; and,   comparing means for comparing at least two image blocks based upon said first and second threshold values so as to obtain coded-image data reflecting said difference in said two averaged values of image concentration.   
     
     
       8. An X-ray imaging system as claimed claim 7, further comprising: a plurality of frame memories each having a plurality of memory regions coupled to said comparing means for storing a plurality of coded-image data derived from said comparing means.   
     
     
       9. An X-ray imaging system as claimed in claim 8, wherein said judging means includes: address generating means for generating a plurality of address data;   first table memory means having a first conversion table, for converting the coded-image data read from each of said plurality of memory regions of each of said plurality of frame memories simultaneously addressed by the same address data into a plurality of code signals based upon the first conversion table;   plural counting means for counting a total number of each of said code signals, while reading all of said plurality of said memory regions of said plurality of frame memories; and   second gable memory means having a second conversion table, for converting said total number o the code signals into a contrast-image present signal based upon the second conversion able, whereby a judgement is made whether or not the X-ray image is acquired under such a condition that the X-ray contrast medium appears therein based upon said contrast-image present signal.   
     
     
       10. An X-ray imaging system as claimed in claim 8, further comprising: one frame memory coupled to said comparing means for storing one piece of said coded-image data.   
     
     
       11. An X-ray imaging system as claimed in claim 10, wherein said judging means includes: address generating means for sequentially generating address data;   code distributing means for distributing code signals reflecting said coded-image data;   plural counting means for counting a total number of each of said code signals while reading an entire memory region of said single frame memory; and,   a table memory having a conversion table coupled to said counting means, for converting said total numbers of code signals into a contrast-image present signal based upon the conversion table, whereby a judgement is established whether the X-ray image is acquired under such a condition that the X-ray contrast medium appears therein based upon the contrast-image present signal.   
     
     
       12. An X-ray imaging system as claimed in claim 7, wherein said threshold value generating means of said calculating means further generates a third threshold value and a fourth threshold value, which are different from said first and second threshold values. 
     
     
       13. An X-ray imaging system as claimed in claim 5, further comprising a peak trace unit including: X-ray image frame memory means for sequentially receiving said plurality of X-ray image to be stored therein; and,   comparator means for comparing said X-ray images with each other which are successively produced by said producing means and derived from said X-ray image frame memory means, so as to obtain X-ray image data having a lowest concentration value from concentration values for all of the compared image data, whereby a plurality of said X-ray image data having the lowest concentration value are continuously derived from said peak trace unit.